A technique of a communication device that includes an orthogonal modulator and an orthogonal demodulator is conventionally disclosed wherein a loop back path that supplies an output of the orthogonal modulator to the orthogonal demodulator is provided and errors of the orthogonal modulator and the orthogonal demodulator are separated by using results of measurement in a case where in-phase local signals are supplied to the orthogonal modulator and the orthogonal demodulator and a case where local signals that have a predetermined phase difference are supplied thereto, so as to compensate for an orthogonal error (a gain error, a phase error, a direct current offset, or the like).
In a case where a phase shift circuit that provides a phase difference to local signals that are supplied to an orthogonal modulator and an orthogonal demodulator is configured by using, for example, an RC filter, gain reduction involved with a phase shift is caused, and hence, an amplitude of a local signal that is supplied to such an orthogonal demodulator varies between before and after such a phase shift to influence an orthogonal error. Therefore, a phase shift circuit is desired where a change of an amplitude of a local signal that is supplied to an orthogonal demodulator between before and after a phase shift is small. Furthermore, in a case where an image signal that is generated from an orthogonal error is eliminated, an image signal component is suppressed by passing through a loop back path due to a frequency characteristic deviation of such a loop back path, so that detection may be executed in a state different from an original orthogonal error. Therefore, an orthogonal error measurement method is desired that is capable of suppressing an influence of a frequency characteristic deviation of a loop back path.